Modeling terrestrial ecosystems: biosphere atmosphere interactions

Transcription

1 Modeling terrestrial ecosystems: biosphere atmosphere interactions Gordon Bonan National Center for Atmospheric Research Boulder, Colorado, USA CLM Tutorial 2014 National Center for Atmospheric Research Boulder, Colorado 18 February 2014 NCAR is sponsored by the National Science Foundation

2 Ecosystems and biogeochemistry 2 An ecological perspective boxes and flows among boxes Odum, E. P. (1971). Fundamentals of Ecology, 3rd edn. Philadelphia: Saunders

3 Ecosystems and biogeochemistry 3 Terrestrial Ecosystem Model (TEM) Raich et al (1991) Ecol. Appl. 1: McGuire et al (1992) GBC 6: CASA Potter et al (1993) GBC 7:

4 Ecosystems and climate 4 Near-instantaneous (30- min) coupling with atmosphere (energy, water, chemical constituents) Long-term dynamical processes that control these fluxes in a changing environment (disturbance, land use, succession) Bonan (2008) Science 320:

5 The Community Land Model (CLM4.5) 5 Fluxes of energy, water, carbon, and nitrogen and the dynamical processes that control these fluxes in a changing environment Oleson et al. (2013) NCAR/TN-503+STR D. Lawrence et al. (2011) JAMES, 3, doi: /2011MS D. Lawrence et al. (2012) J Climate 25: Spatial scale 1.25 longitude latitude ( grid) Temporal scale 30-minute coupling with atmosphere Seasonal-to-interannual (phenology) Decadal-to-century climate (disturbance, land use, succession) Paleoclimate (biogeography)

6 Earth system models 6 Earth system models use mathematical formulas to simulate the physical, chemical, and biological processes that drive Earth s atmosphere, hydrosphere, biosphere, and geosphere A typical Earth system model consists of coupled models of the atmosphere, ocean, sea ice, and land Land is represented by its ecosystems, watersheds, people, and socioeconomic drivers of environmental change (IPCC 2007) Prominent terrestrial feedbacks Snow cover and climate Soil moisture-evapotranspiration-precipitation Land use and land cover change Carbon cycle Reactive nitrogen The model provides a comprehensive understanding of the processes by which people and ecosystems feed back, adapt to, and mitigate global environmental change

7 Evolution of climate science 7 Atmospheric sciences Atmospheric general circulation models Atmospheric physics and dynamics Prescribed sea-surface temperature and sea ice Bulk formulation of surface fluxes without vegetation Bucket model of soil hydrology (1970s) Land surface models Surface energy balance Hydrologic cycle Plant canopy (1980s) Oceanography Ocean general circulation models Physics, dynamics Atmospheric & oceanic sciences Global climate models Atmosphere Land and vegetation Ocean Sea ice (1990s) Ecology Terrestrial ecosystem models Biogeochemical cycles (C-N-P) Vegetation dynamics Wildfire Land use (early 2000s) Earth system models Physics, chemistry, biology Humans, socioeconomics Ocean ecosystem models Biogeochemical cycles Earth system science (2010s)

8 Planetary stressors 8 It is not just greenhouse gases anymore CO 2 concentration Forest area N deposition Global mean temperature P. Lawrence et al. (2012) J Climate 25: P. Lawrence et al. (2012) J Climate 25: Forcings Solar variability & volcanic aerosols CO 2, N 2 O, CH 4, aerosols, stratospheric ozone N deposition Land use (land cover change, wood harvest) Aerosol deposition on snow (black carbon) Tropospheric ozone Fertilizer & manure

9 Planetary distress drought, Waterloo, NE (Nati Harnik, AP) Sea ice retreat (Jonathan Hayward/CP file photo, Habitat loss, NM (UCAR) Pine beetle, CO (RJ Sangosti/Denver Post) High Park fire, CO (RJ Sangosti/Denver Post) Coastal flooding, NC (U.S. Coast Guard) Texas drought ( Calving face of the Ilulissat Isfjord, Greenland, 7 June 2007 ( Midway-Sunset oil field, CA (Jim Wilson/The New York Times) It is not just atmospheric physics and dynamics

10 The Anthropocene 10 Population of the world, , according to different projection variants (in billion) Human activities (energy use, agriculture, deforestation, urbanization) and their effects on climate, water resources, and biogeochemical cycles What is our collective future? Can we manage the Earth system, especially its ecosystems, to create a sustainable future? Source: United Nations, Department of Economic and Social Affairs, Population Division (2009): World Population Prospects: The 2008 Revision. New York

11 Terrestrial ecosystems and global environmental change 11 Land as the critical interface through which people affect, adapt to, and mitigate global environmental change Expanded capability to simulate ecological, hydrological, biogeochemical, and socioeconomic forcings and feedbacks in the Earth system Increased emphasis on impacts, adaptation, and mitigation Requires an integrated assessment modeling framework Human systems (land use, urbanization, energy use) Biogeochemical systems (C-N-P, trace gas emissions, isotopes) Water systems (resource management, (IPCC 2007) freshwater availability, water quality) Ecosystems (disturbance, vulnerability, goods and services)

12 Ecosystems and climate policy 12 Boreal forest menace to society no need to promote conservation Temperate forest reforestation and afforestation Biofuel plantations to increase albedo and reduce atmospheric CO 2 Tropical rainforest planetary savior promote avoided deforestation, reforestation, or afforestation These comments are tongue-in-cheek and do not advocate a particular position

13 Understanding Earth s climate system 13 Forcings Forcings: drivers of system change Solar irradiance Volcanic aerosols Anthropogenic aerosols CO 2 concentration Feedbacks: amplify or dampen system response Water vapor Clouds Snow-ice albedo Ocean heat uptake Feedbacks Natural variability ENSO, NAO PDO Global temperature ( C) Response Meehl et al. (2004) J Climate 17:

14 C4MIP Climate and carbon cycle ppm 730 ppm 11 Pg C yr -1 Carbon cycle-climate feedback 11 carbon cycle-climate models of varying complexity CO 2 fertilization enhances carbon uptake, diminished by decreased productivity and increased soil carbon loss with warming Large uncertainty: 290 ppm difference in atmospheric CO 2 at Pg C yr -1 difference in land uptake at 2100 Friedlingstein et al. (2006) J Climate 19: Pg C yr -1

15 Uncertainty in feedback is large 15 C L = β L C A + γ L T β L > 0: concentration-carbon feedback (Pg C ppm -1 ) γ L < 0: climate-carbon feedback (Pg C K -1 ) Concentration-carbon feedback Climate-carbon feedback β L =1.4 Pg C ppm -1 [ ] γ L =-79 Pg C K -1 [-20 to -177] CO 2 fertilization enhances carbon uptake Carbon loss with warming Friedlingstein et al. (2006) J Climate 19:

16 CMIP5 Climate and carbon cycle 16 Carbon cycle-climate feedback 9 Earth system models of varying complexity 140-year simulations during which atmospheric CO 2 increases 1% per year from ~280 ppm to ~1120 ppm Arora et al. (2013) J Climate 26: Cumulative land-atmosphere CO 2 flux (Pg C) Fully coupled Climate-carbon coupling Concentration-carbon coupling Carbon-only models C-N model Years Years Years CMIP5: C4MIP: γ L =-58 Pg C K -1 [-16 to -89] β L =0.9 Pg C ppm -1 [ ] γ L =-79 Pg C K -1 [-20 to -177] β L =1.4 Pg C ppm -1 [ ]

17 CLM4 carbon cycle 17 Cumulative land-atmosphere CO 2 flux (Pg C) 250 Carbon accumulation (Pg C) CO2 C-N Carbon-only CO2 & climate CO2 CO2 & climate C_s1 C_s2 CN_s1 CN_s

18 CLM4.5 carbon cycle 18 Cumulative land-atmosphere CO 2 flux (Pg C) Koven et al. (2013) Biogeosciences 10:

19 Global land use 19 Local land use is spatially heterogeneous NSF/NCAR C-130 aircraft above a patchwork of agricultural land during a research flight over Colorado and northern Mexico Global land use is abstracted to the fractional area of crops and pasture Foley et al. (2005) Science 309:

20 Historical land use & land cover change, Change in tree and crop cover (percent of grid cell) Cumulative percent of grid cell harvested Historical LULCC in CLM4 Loss of tree cover and increase in cropland Farm abandonment and reforestation in eastern U.S. and Europe Extensive wood harvest P. Lawrence et al. (2012) J Climate 25:

21 Land use carbon flux 21 Carbon perspective Land use is a source of carbon to the atmosphere

22 Land use forcing of climate 22 The emerging consensus is that land cover change in middle latitudes has cooled the Northern Hemisphere (primarily because of higher surface albedo in spring) Northern Hemisphere annual mean temperature decreases by 0.19 to 0.36 C relative to the pre-industrial era Mean annual air temperature, NH (ºC) Comparison of 6 EMICs forced with historical land cover change, Brovkin et al. (2006) Clim Dyn 26:

23 Surface albedo 23 Maximum snow-covered albedo LULCC effects Vegetation masking of snow High albedo of crops Monthly surface albedo (MODIS) by land cover type in NE US 0.6 Barlage et al. (2005) GRL, 32, doi: /2005gl Albedo Higher summer albedo 0.2 Forest masking Colorado Rocky Mountains Jackson et al. (2008) Environ Res Lett, 3, (doi: / /3/4/044006)

24 Land cover change and evapotranspiration 24 Prevailing model paradigm Crops & grasses Low latent heat flux because of: o Low roughness o Shallow roots decrease soil water availability Trees High latent heat flux because of: o High roughness o Deep roots allow increased soil water availability Dry soil Wet soil Tropical forest cooling from higher surface albedo of cropland and pastureland is offset by warming associated with reduced evapotranspiration Temperate forest - higher albedo leads to cooling, but changes in evapotranspiration can either enhance or mitigate this cooling Bonan (2008) Science 320:

25 Forests influences on global climate 25 Annual mean surface temperature change ( C) Davin & de Noblet-Ducoudré (2010) J Climate 23: Prevailing biogeophysical paradigm Boreal and temperate forests warm climate Tropical forests cool climate

26 LULCC relative to greenhouse warming 26 Multi-model ensemble of the simulated changes between the pre-industrial time period and present-day North America Eurasia CO 2 + SST + SIC forcing leads to warming LULCC leads to cooling de Noblet-Ducoudré, Boiser, Pitman, et al. (2012) J Climate 25: The bottom and top of the box are the 25th and 75th percentile, and the horizontal line within each box is the 50th percentile (the median). The whiskers (straight lines) indicate the ensemble maximum and minimum values. Key points: The LULCC forcing is counter to greenhouse warming The LULCC forcing has large intermodel spread, especially JJA

27 Land use choices affect 21st century climate 27 Future IPCC SRES land cover scenarios for NCAR LSM/PCM B1 - Loss of farmland and net reforestation due to declining global population and farm abandonment in the latter part of the century A2 - Widespread agricultural expansion with most land suitable for agriculture used for farming by 2100 to support a large global population Feddema et al. (2005) Science 310:

28 Climate outcome of land use choices 28 Change in temperature (JJA) due to land cover SRES B1 SRES A B1 Weak temperate warming Weak tropical warming A2 Temperate cooling Tropical warming Feddema et al. (2005) Science 310:

29 Biogeophysical vs. biogeochemical interactions 29 Prevailing paradigm The dominant competing signals from historical deforestation are an increase in surface albedo countered by carbon emission to the atmosphere Change in annual surface temperature from anthropogenic LULCC over the 20th century Biogeophysical Weak global cooling (-0.03 C) Biogeochemical Strong warming ( C) Net Warming ( C) Pongratz et al. (2010) GRL,37, doi: /2010gl043010

30 Future land cover change 30 A2 biogeophysical B1 biogeophysical Biogeophysical A2 cooling with widespread cropland B1 warming with temperate reforestation Biogeochemical A2 large warming; widespread deforestation B1 weak warming; less tropical deforestation, temperate reforestation A2 biogeochemical B1 biogeochemical Net effect similar A2 BGC warming offsets BGP cooling B1 moderate BGP warming augments weak BGC warming A2 net B1 net Sitch et al. (2005) GBC, 19, GB2013, doi: /2004gb002311

31 Community Earth System Model CMIP5 simulations 31 Full transient (all forcings) Land cover change only Historical changes in annual surface albedo and temperature (1850 to 2005) P. Lawrence et al. (2012) J Climate 25: Key points: LULCC forcing is counter to all forcing LULCC forcing is regional, all forcing is global

32 Opposing trends in vegetation 32 Historical changes in annual leaf area index (1850 to 2005) Single forcing simulation Land cover change only Loss of leaf area, except where reforestation All forcing simulation CO 2 Climate Nitrogen deposition Land cover change Increase in leaf area, except where agricultural expansion P. Lawrence et al. (2012) J Climate 25:

33 21st century land use & land cover change 33 Description RCP Largest increase in crops. Forest area declines. RCP Largest decrease in crop. Expansion of forest areas for carbon storage. RCP Medium cropland increase. Forest area remains constant. RCP Medium increases in cropland. Largest decline in forest area. Biofuels included in wood harvest. P. Lawrence et al. (2012) J Climate 25:

34 Twenty-first century forests 34 Change in tree cover (percent of grid cell) over the 21st century P. Lawrence et al. (2012) J Climate 25:

35 Twenty-first century cropland 35 Change in crop cover (percent of grid cell) over the 21st century P. Lawrence et al. (2012) J Climate 25:

36 Carbon cycle 36 LULCC carbon flux to atmosphere Land use choice matters RCP 4.5 : reforestation drives carbon gain RCP 8.5 : deforestation and wood harvest drive carbon loss P. Lawrence et al. (2012) J Climate 25:

37 Nitrogen cascade and climate 37 Science NH x NO y Increasing emissions of nitrogen oxides (NO x ), ammonia (NH 3 ), and nitrous oxide (N 2 O) alter atmospheric composition and chemistry N 2 O, O 3, CH 4, and aerosols Deposition of NH x and NO y on land alters ecosystems Carbon storage, biodiversity Indirect effects, e.g., higher surface 0 3 reduces plant productivity Policy Nitrogen management strategies for global climate change mitigation, and concomitant benefits to society through the N cascade

38 Effect of additional N on global mean radiative forcings IPCC 2007: WG1-AR4 Nitrogen addition: Change in radiative forcing Increases land CO 2 uptake (-) N 2 O emission: Increases N 2 O (+) NO X emission: Decreases CH 4 (-) NO X emission: Increases tropospheric O 3 (+) N 2 O emission: Decreases stratospheric O 3 (+) NH 3 emission: Increases aerosols (-) 38 Cooling Warming Nitrogen addition alters the composition and chemistry of the atmosphere, and changes the radiative forcing. The net radiative forcing varies regionally.

39 Terrestrial ecosystems and global environmental change 39 Multiple competing influences of forests albedo, ET, C, and also Nr, aerosols Bonan (2008) Science 320: Credit: Nicolle Rager Fuller, National Science Foundation